Many household appliances and light industry apparatus utilize cordless power supplies such as batteries. In recent years the rechargeable or secondary battery has emerged as a prime power supply for such devices and with the increase of battery operated toys, power tools and the like, new demands have been made not only for rechargeable batteries, but also for charging units. The basic requirement for a battery charging unit is a source of direct current having a voltage higher than that of a fully charged battery. Many techniques for charging secondary batteries are known, and the circuit components employed in such techniques are usually determined by the amount of control desired over the charging current and/or voltage. For different type secondary batteries, the charging current and voltage requirements are different. Secondary batteries are usually specified with a specific charge rate in terms related to the ampere-hour capacity. The charge rate in amperes is determined by dividing the battery capacity in ampere hours by the desired time of charging in hours; for example, 10 hours, but charging for a somewhat longer time or higher current is usually employed to insure full capacity discharge from the battery. Charge rates in commercial use today range from about a one hour rate to about a 30-hour rate.
Most of today's secondary battery units a "self-discharge" characteristic; and consequently, when a battery is left on a shelf for a long period of time, it will gradually lose charge or capacity. To maintain a battery in a peak charge condition, it may be advisable to charge the battery on a very low charge rate referred to as a trickle charge. Of course, the trickle rate may vary with different battery units but generally the trickle rate would be about a 20 hour rate.
Recent nickel-cadmium cells and batteries have been developed that can take a fast charge at a one-hour rate or less. Thus with the use of fast charge cells, shorter recharging times can be used. Various proposals made for charging secondary nickel-cadmium cells and batteries at high rates require some sort of fail safe means for terminating the high rate charge. If overcharge is continued at too high a rate of charge current, the oxygen gas, which normally reacts or combines with the active cadmium metal on the surface of the negative electrodes, known as the "oxygen recombination" principle, may not fully recombine and consequently result in an excessive internal gas pressure build up. This could not only damage the cell but could cause the cell under certain conditions to disassemble. One proposal for minimizing overcharge is to incorporate a pressure operated switch in the cell which would automatically cut off the charging current when the internal gas pressure reaches a predetermined level. Another proposal entails the incorporation of an oxygen-consuming auxiliary electrode in the cell to consume the oxygen gas as it evolves thereby preventing the build up of excessive internal gas pressure.
Thus it is necessary to insure that a fast charge at a high rate of current is not employed to charge batteries that should be charged at lower current rates. Fast charge rate batteries may employ temperature sensing means to detect the temperature rise of the battery, or use external voltage sensing means to detect the voltage of the battery during charging, both means of which are indicative of the charge condition of the battery. These means can be used to terminate a charging operation to prevent overcharge of the battery.
U.S. Pat. No. 4,628,243 discloses a battery charging system provided with means for detecting special indicia on the battery so that only batteries with this special indicia can be charged by the system. Thus only cells with the special indicia can be charged using this battery charging system.
U.S. Pat. No. 3,506,902 discloses the use of a separate, circumferential charging terminal positioned on a rechargeable battery so that a charger will only charge a rechargeable battery that is designed with this separate circumferential charging terminal. The separate terminal may be formed by cutting away a portion of the cell's insulation wrapper to expose an area of its conductive casing which can be used as the separate charging terminal.
U.S. Pat. No. 4,489,268 discloses a battery that employs a separate charging terminal contact that is spaced apart from the external power terminals so that such charging terminal contact can engage a corresponding charging contact positioned in a battery charger.
It is an object of the present invention to provide a rechargeable battery with an indicator band that can be sensed by a charging device so that a specific preferred charge rate can be applied to the rechargeable battery depending on the location of the indicator band on the battery.
Another object of the present invention is to provide a charging device that senses the presence of an indicator band on a rechargeable battery and then provides a specific preferable charge rate to the rechargeable battery depending on the location of the indicator band.
Another object of the present invention is to provide a battery charger for use with a rechargeable battery that is designed with an indicator band, the location of which determines the preferred rate of current that should be used to charge the rechargeable battery.
Another object of the present invention is to provide a rechargeable battery for use in a battery charger device designed to provide at least two different rates of charging current, said rechargeable battery having a positive terminal and a spaced-apart negative terminal for delivering power to an external device and also having an indicator band on the battery, the location of which is indicative of the specific rate of charge the battery can safely accept.
Further objects and advantages of the invention, as well as modifications obvious to those skilled in the art, will become apparent from the following description taken in conjunction with the accompanying drawings.